The project is designed to examine protein inhibitors of ribonuclease activity in various human tissues. In order to better understand any role they might play in controlling ribonuclease levels in the serum and urine of cancer patients. RNase A affinity chromatography has proven to be the most effective means of isolating the inhibitors from tissue homogenates of liver, brain, and heart. The protein inhibitors will be characterized and compared to polynucleotide inhibitors for effectiveness in reducing hydrolytic activity of ribonuclease.